The present invention relates to a polishing composition used to polish semiconductor substrates such as a silicon wafer.
As design rules for semiconductor devices have been demanding finer patterning and processing on the substrates year by year, it has been increasingly required that a bare silicon wafer should have only a few number of flaws and high smoothness. A concave defect designated as a crystal originated particle (COP) or haze has been known as an index for evaluating surface properties of a silicon wafer. COP is generated on the surface of a silicon wafer due to crystal defects regarding a monocrystal silicon as a material for a silicon wafer, or due to scratches caused by a polishing agent. Haze is opalescent fogging that can be observed by visual observation when strong light is applied to the surface of a silicon wafer in a darkroom.
Japanese Laid-Open Patent Publication No. 2001-110760, for example, discloses a polishing composition that is improved to respond to such requirements. This polishing composition comprises a polishing material such as colloidal silica, an auxiliary polishing agent containing block polyether represented by the chemical formula HO—(PO)d—(EO)e—(PO)f—H, and water. In the above chemical formula, PO represents an oxypropylene group, EO represents an oxyethylene group, and each of d, e, and f represents an integer of 1 or greater. The use of this polishing composition reduces haze observed on the surface of a silicon wafer after polishing to a certain extent. This is because the surface tension of the polishing composition is changed to be suitable for polishing a wafer by the action of the auxiliary polishing agent.
However, the performance of this polishing composition is not sufficient for satisfying the requirements of users regarding haze, and more improvements should be made. In addition, this polishing composition does not have a high ability to polish a silicon wafer. In other words, this polishing composition does not have an ability to rapidly polish a silicon wafer. Moreover, this polishing composition makes almost no contribution to a reduction in the number of COP observed on the surface of a silicon wafer after polishing.